Modern user devices such as smartphones, tablets, notebooks, electronic readers and the like typically include, in addition to wireless communication capabilities, one or more sensors that can detect and/or infer the context of the device and, by extension, contextual information of the user. One example is the use of a position or location determining sensor such as a global positioning system (GPS) receiver.
In addition to the large amount of personal data stored on these user devices (messaging logs, call logs, contacts list, etc.) many sensors can be used to infer the location, context, personal habits, etc. of the user. This information may be exposed to privacy threats from third party applications that the user installs, but does not necessarily trust. Such third party applications may record and share personal information without the user's consent. On the other hand, given the value of such information for service providers, the user himself may be interested in sharing private data with service providers for an appropriate benefit or price, while still protecting his or her privacy to a desired degree.